The RUC Chief Constable says police are pursuing a line of inquiry that local elements of the Loyalist Volunteer Force were involved in the murder of journalist Martin O'Hagan.
But Sir Ronnie Flanagan says it has not been firmly established who is responsible for the killing.
He spoke during the launch of a RUC-sponsored human rights conference in Belfast.
He said, "It would be wrong at this stage of the investigation to use the words that it has been firmly established who is responsible for this horrific killing.
"Certainly, there has been much speculation about this murder and we would have to acknowledge that there have been links between the Loyalist Volunteer Force and the Ulster Defence Association through certain individuals.
"However at this stage there is nothing to suggest definitively who was responsible."
The Chief Constable added that the loyalist groups' ceasefires were being kept under constant review.
The government, he noted, had given the UDA one final chance to demonstrate what they are capable of in terms of maintaining a ceasefire.
"I have no doubt that the Secretary of State will be keeping a very close eye on Loyalist Volunteer Force activity on a daily basis."
O'Hagan, 51, who worked for the northern edition of the Sunday World, was shot dead as he walked home with his wife Marie from their local pub in Lurgan, Co Armagh.
His funeral takes place this afternoon.